Fluid heating by radiation

ABSTRACT

Radiant energy is used to heat a liquid by passing the liquid between two level, flat, heat exchange surfaces, the top surface resting freely on the lower surface and being exposed to the radiant energy. Liquid flows between the surfaces and is maintained in a thin, continuous and substantially uniform film by operation of Bernoulli&#39;&#39;s Theorem. In a preferred embodiment, water is heated by solar radiation and the heat exchange surfaces float on a reservoir of the water being heated.

United States Patent William B. Harris. .Ir.

Huntsville;

William B. Harris, Bryan: Richard R. Davison, Bryan, all of Tex.

Mar. 24, 1970 Nov. 16, 1971 The United States of America as representedby the Secretary of the Interior inventors Appl. No Filed PatentedAssignee FLUID HEATING BY RADIATION l 1 Claims, 3 Drawing Figs.

U.S. Cl Int. Cl Field of Search References Cited UNITED STATES PATENTS9/1964 Yellott 126/271 3,200,820 8/1965 Garrett 126/271 3.077.190 2/1963Allen 126/271 3.215.134 11/1965 Thomason 126/271 3.252.456 5/1966 Bohn..Ir. 126/271 FOREIGN PATENTS 994.106 8/1951 France 126/271 PrimarExaminer-Charles J1 Myhre Auorneys- Ernest S. Cohen and Roland H.Shubert ABSTRACT: Radiant energy is used to heat a liquid by passing theliquid between two level. flat. heat exchange surfaces. the top surfaceresting freely on the lower surface and being exposed to the radiantenergyv Liquid flows between the surfaces and is maintained in a thin.continuous and substantially uniform film by operation of BernoullisTheorem. in a preferred embodiment. water is heated by solar radiationand the heat exchange surfaces float on a reservoir of the water beingheated PATENTEDuov 16 I97! 3, 620,206

SHEET 1 [IF 2 INVENTORS' WILLIAM B. HARRIS, JR.

WILL/AM B. HARE/5,5)? RICHARD H. DAV/SON ATTORNEYS PATENTEDNUV 15 Ian3,620,206 sum 2 OF 2 FIGS lNl/E/VTORS W. 1. MM 8. HARRIS, JR. WILL/AM B.HARRIS, 5R. RICHARD 6. DA V/SON AT TORNEYS FLUID HEATING BY RADIATIONBACKGROUND OF THE INVENTION Solar energy has long been used as a sourceof heat for a variety of purposes. A number of different types of solarwater heaters have been developed for domestic heating, heating swimmingpools, for desalination processes and other processes which can utilizelow-grade heat energy.

Previous designs of solar water heaters have suffered from a number ofdefects. Many designs, such as those incorporating plastic filmconstruction, lack durability. Many durable heater designs, such as someproposed and utilized for building heating, have been too expensive forextensive use. Many of the previous heaters suffered from lowefficiency, lacked quickness of response to changing solar conditionsand displayed excessive night heat loss.

SUMMARY OF THE INVENTION It has now been found that a device for theextraction of heat from radiant energy which utilizes the effect ofBemoullis Theorem increases efficiency of the device and allows moresensitive and faster response to changing levels of incident radiation.In its simplest form, a heat exchange liquid is passed between tworelatively rigid, flat surfaces; the top surface being exposed toincident radiation and resting freely on the lower surface. The uppersurface is substantially transparent to radiation while the lowersurface absorbs radiation. As required by Bernoulli's Theorem, liquidpassing between the two surfaces is in the form of a compressed,continuous and relatively uniform film.

In a preferred embodiment of the invention, water is heated by solarradiation. The two surfaces making up the heat extracting portion of thedevice float on the surface of water storage or reservoir means whilethe flow of water between the surfaces is controlled responsive to theincident solar radiation.

Hence it is an object of this invention to provide a method and meansfor extraction of heat from radiant energy.

It is a specific object of this invention to provide a solar waterheater having characteristics of high efficiency, lowheat loss andsensitive response to incident radiation intensity.

It is a further object of this invention to provide a process for therecovery of heat from incident solar radiation.

DETAILED DESCRIPTION OF THE INVENTION The invention will be more clearlyunderstood by reference to the accompanying drawings in which:

FIG. 1 represents a diagrammatic view of the heat extracting system ofthis invention.

FIG. 2 is an oblique, exploded view of a preferred embodiment of asingle heat exchange module.

FIG. 3 is a partial sectional view of a multimodule heat exchange deviceconstructed in accordance with the invention.

Referring now to FIG. 1, the heat exchange device, generally designatedby the numeral 1, comprises a relatively rigid and flat basal member 2disposed in a substantially horizontal attitude. Resting on the basalmember and conforming generally to the size and shape of that member iscover plate 3. Liquid from supply or storage means 4 passes throughconduit 5 to pump 6. From pump 6, the liquid is passed, via conduit 7,to a centralarea between basal member 2 and cover plate 3. Liquid thenflows outwardly toward the periphery of the basal member and cover platein a thin channel 8 formed between the two. Liquid is recovered incollecting means 9 and is returned to storage means 4 by means ofconduit 10.

By operation of Bernoullis Theorem, liquid flowing through channel 8 ismaintained as a compressed, thin and evenly distributed film. Asrequired by that Theorem, if liquid flow tended to channel in onedirection, the increased rate of flow would reduce the pressure in thechannelling areaReduction in pressure would in turn cause the coverplate to press more tightly on the basal member in that area thusdiverting excess flow to areas of lower flow rate. While FIG. 1 showsliquid being introduced through a central. portion of the basal member,this is not necessary to proper functioning of the device. It is alsopossible to introduce liquid at an edge, but this is a less effectiveand less preferred arrangement.

In operation, cover plate 3 is exposed to an external heat flux such assolar radiation. Liquid, such as water. is passed through the heatexchange device as previously described. The heated liquid may be usedfor any conventional and appropriate purpose; may be in turnheat-exchanged with another liquid or gas, or may be used as storagemeans for heat energy.

When the source of external heat flux is variable, such as is solarradiation, radiation-sensitive control device I] may be connected bymeans of control wires 12 to control the operation of pump 6.Controlling liquid flow through the heat exchange device responsive toexternal heat flux changes permits almost instantaneous response tononheat gain conditions. This rapid response time coupled with the verysmall quantity of liquid exposed to heat exchange conditions results inlarge efiiciency gains.

Turning now to FIG. 2, there is shown an oblique, exploded view of onepreferred embodiment of this invention. In this embodiment, basal member2 is constructed of a material, such as foam glass, having insulatingproperties and having a specific gravity less than that of the liquidbeing circulated. Cover plate 3 comprises a relatively flat andtransparent material resting directly on the basal member and conformingin size and shape to that member. Plate 3 may be constructed of glass,plastic sheet or plastic film. Generally, a rigid material such as glassis preferred. A second transparent member I3 forms in cooperation withspacer 14 an insulating, dead airspace. Member 13 may comprise a glassplate or may comprise plastic film or similar materials. Liquid isdelivered to a central point on the upper surface of basal member 2.Moving liquid forms a thin, relatively uniform film between member 2 andplate 3 and overflows at the edge portions of these two members. Theupper surface of member 2 preferably is treated with a dark, heatabsorbing coating as is well known in the art.

FIG. 2 represents a single module or unit. When assembled in amultimodule configuration, spacer pegs 15 are provided on the edges ofbasal member 2. These spacer pegs provide a return channel for theliquid after it is passed through the heat exchange portion of thedevice. A liquid collection tray may be provided at a level beneathbasal member 3 or, in a preferable embodiment, the return channelscommunicate directly with a liquid storage area. This last embodiment isillustrated in FIG. 3.

FIG. 3 represents a partial sectional view of a multimodule heatexchange device in accordance with the invention. Liquid storage means20, preferably constructed of a material having heat-insulatingproperties, is substantially completely filled with the liquid to beheat exchanged. Floating on and supported by the liquid are a pluralityof heat exchange modules such as are represented in FIG. 2.

Each module comprises a buoyant, basal member 2, a cover plate 3, spacermeans 14 and a second transparent member 13. Buoyant basal member 2 ispreferably constructed of a material such as foam glass. However, othermaterials and methods of construction may also be used. For example,member 2 may be constructed of metal or other suitable materials in theform of a flat, hollow, or buoyant-plastic foam-filled float. Spacerpegs I5 maintain the modules in a somewhat separated position thusproviding return channels 21 to allow liquid to return to the storagearea. Sealing means 22, which may conveniently comprise flexible stripsof the configuration, isolate the system from the external environment.Liquid is circulated from a lower region of storage means 20 throughconduit 5 to pump 6. Pump 6 then distributes liquid via conduits 7 tothe central portions of individual heat exchange modules where theliquid is heated by incident radiation striking basal member 2. Asillustrated in FIG. 1, the operation of pump 6 is preferably controlledby a radiation-sensitive control device so that the pump operates onlyduring periods in which incident radiation is of sufficient intensity tocause heating of the circulating liquid. A number of conventionalsensors, including thermistors and photosensitive devices of many kinds,may readily be adapted for this purpose.

Heat developed and stored by this system may be used to furnish energyfor heating, drying, solvent extraction, desalination or any otherprocess which can utilize heat at temperatures below the boiling pointof water. Utilization of the heat energy can be accomplished in anyconventional fashion. For example, a secondary heat exchanger may beplaced within the liquid stored in means 20. A stream of heated liquidmay also be transported from means 20 to a point of utilization. Othermeans and methods for utilizing the heat energy will be readily apparentto those skilled in the art.

Tests of single and multimodule units, constructed in general accordancewith FIG. 3, were performed using solar energy as the source of incidentheat flux and water as the liquid medium. Efficiencies as high as about65 percent of theoretical were attained by these units. Efiiciency inthis case is defined as gain divided by input multiplied by 100. lnputis a measure of local radiant energy available as measured by a devicesuch as the Eppley pyrheliometer while gain is measured by the increasedheat content of the circulating water.

What is claimed is:

l. A device for extracting heat from incident radiant energy comprising:

a. a basal, relatively rigid, flat member normally disposed in asubstantially horizontal attitude;

b. a flat, relatively rigid plate conforming generally to the size andshape of the basal member and resting on that member, said plate beingadapted for exposure to incident radiant energy;

c. means to pass a liquid between the basal member and the plate; and

d. means at the periphery of the plate and basal member to recover theliquid.

2. The device of claim 1 wherein the top surface of the basal member isadapted to absorb radiant energy.

3. The device of claim 2 wherein the basal member is constructed of amaterial having thermal insulation properties and having buoyancyrelative to said liquid.

4. The device of claim 3 wherein the plate is substantially transparentto the incident radiant energy.

5. The device of claim 4 wherein liquid storage means are disposed belowsaid basal member.

6. The device of claim 5 wherein the basal member is buoyantly supportedon the surface of the liquid in said storage means.

7. The device of claim 6 including sensing means adapted to control thepassage of liquid between the basal member and the plate responsive tothe intensity of incident radiation.

8. The device of claim 7 including a second transparent member spacedabove the plate and forming in cooperation with that plate an insulatingdead air space.

9. The device of claim 8 including spacer means on the periphery of saidbasal member to provide a channel for liquid to return to said storagemeans.

10. A process for heating water by means of solar radiation whichcomprises passing a flow of water between two relatively rigid, flatsurfaces, said surfaces being disposed in a substantially levelattitude, the bottom surface comprising a radiation absorbing member andthe upper surface comprising a radiation transmitting member, the uppersurface being freely supported by the bottom surface, therebymaintaining a compressed, continuous and substantially uniform flowingfilm of water between the two surfaces.

11. The process of claim 10 wherein the flow of water between the twosurfaces is controlled responsive to the intensity of incident solarradiation s trik ing the upper surface.

1. A device for extracting heat from incident radiant energy comprising:a. a basal, relatively rigid, flat member normally disposed in asubstantially horizontal attitude; b. a flat, relatively rigid plateconforming generally to the size and shape of the basal member andresting on that member, said plate being adapted for exposure toincident radiant energy; c. means to pass a liquid between the basalmember and the plate; and d. means at the periphery of the plate andbasal member to recover the liquid.
 2. The device of claim 1 wherein thetop surface of the basal member is adapted to absorb radiant energy. 3.The device of claim 2 wherein the basal member is constructed of amaterial having thermal insulation properties and having buoyancyrelative to said liquid.
 4. The device of claim 3 wherein the plate issubstantially transparent to the incident radiant energy.
 5. The deviceof claim 4 wherein liquid storage means are disposed below said basalmember.
 6. The device of claim 5 wherein the basal member is buoyantlysupported on the surface of the liquid in said storage means.
 7. Thedevice of claim 6 including sensing means adapted To control the passageof liquid between the basal member and the plate responsive to theintensity of incident radiation.
 8. The device of claim 7 including asecond transparent member spaced above the plate and forming incooperation with that plate an insulating dead air space.
 9. The deviceof claim 8 including spacer means on the periphery of said basal memberto provide a channel for liquid to return to said storage means.
 10. Aprocess for heating water by means of solar radiation which comprisespassing a flow of water between two relatively rigid, flat surfaces,said surfaces being disposed in a substantially level attitude, thebottom surface comprising a radiation absorbing member and the uppersurface comprising a radiation transmitting member, the upper surfacebeing freely supported by the bottom surface, thereby maintaining acompressed, continuous and substantially uniform flowing film of waterbetween the two surfaces.
 11. The process of claim 10 wherein the flowof water between the two surfaces is controlled responsive to theintensity of incident solar radiation striking the upper surface.